1. Field of the Invention
This invention generally relates to an air intake control device. More specifically, the invention relates to a throttle body in an internal combustion engine having a dual bore throttle body.
2. Related Technology
Throttle bodies regulate the airflow to an internal combustion engine where the air is mixed with gasoline. Internal combustion engines require a precise mixture of air and gasoline in order to run properly, and therefore throttle bodies are designed to adjustably control the airflow into the cylinders of the engine. In order to control the airflow that reaches the cylinders, the throttle body includes at least one throttle plate (hereinafter “plates”) attached to a throttle shaft and configured such that each throttle plate is located within the throttle bores, or proximal to an end of each of the throttle bores. With rotation of the shaft, the throttle plates are able to selectively obstruct airflow through the throttle bores. More specifically, the throttle plates are able to rotate with respect to each of the bores in order to adjust the cross-sectional area of the bores that is not obstructed by the plates (the “effective area”), thus controlling the airflow that is permitted to flow through the throttle bores.
In order to effectively control the effective areas of the bores, the throttle plates are sized and shaped approximately the same as the cross-sections of the bores in order to completely or substantially obstruct the bores when a throttle plate is substantially perpendicular to the airflow (the “closed position”). Additionally, the throttle plates have a minimal thickness in order to not substantially obstruct the throttle bores when the plates are angled such that a throttle plate face is not substantially perpendicular to the airflow (the “open position”).
During operation, when the engine is idling, the throttle plates are in the closed position because very little air is needed to mix with the small amount of fuel being injected into the engine. Conversely, the throttle plates are in a variety of open positions at operating speeds higher than idle because more air is needed to mix with the increased amount of fuel being provided to the engine.
When the throttle plates are closed, pressure builds on the upstream face of the throttle plate, which is the side of the plate that is closer to the air intake when the throttle plate is closed. If the pressure on the upstream face of the throttle plate is high enough, it may cause the shaft to deflect towards the engine, which can cause unwanted contact between throttle body components, excessive friction between moving parts, and premature part failure.
Plural-bore throttle bodies, such as dual-bore throttle bodies, are more susceptible to shaft deflection and premature part failure than single-bore throttle bodies due to length and the positioning of the dual-bore throttle shaft. Dual-bore throttle bodies include two bores and two throttle plates configured side-by-side on a common shaft. Thus, a dual-bore throttle shaft is approximately twice as long as a single-bore throttle shaft. Longer throttle shafts have a greater tendency to deflect than shorter throttle shafts. Additionally, dual-bore throttle bodies include a housing that forms the bores, and the housing typically includes an opening for rotatably receiving the approximate mid-point of the shaft. As with any rigid body, the shaft undergoes maximum deflection near its mid-point. Therefore, dual-bore throttle bodies are particularly susceptible to excessive wear at the point of contact between the throttle shaft mid-point and the housing support opening between the two bores.
Therefore, it is desirous to minimize both the throttle shaft deflection and the friction between moving parts.